HYMENOPTEROUS PARASITES. 281 



The genus Brachinostemma and several genera (e.g. Baryconus, 

 Probaryconus, Ceratoteleia, Caloteleia, Ceratob^eus, etc.) of the 

 closely allied family Scelionidae show a tubercle or very short horn 

 arising from the dorsum of the first abdominal segment, but in no case 

 does this ever attain a development approaching that seen in Ino- 

 stemma. From the apparently rudimentary development of what is 

 seemingly homologous to the horn in Inostemma, one might readily 

 conclude that these genera show it in an incipient stage. From the 

 standpoint of function this does not seem possible, however, as the 

 projection is often so short that it does not serve to lengthen the space 

 within the abdomen. Possibly the tubercle or horn may have been 

 developed for some other reason and later served for the accommoda- 

 tion of the ovipositor. The long horn appears to be unique, however, 

 and no one has so far been able to attribute to it any other function. 

 We may readily suppose that its ontogenesis is in direct response to 

 pressure produced by the base of the developing ovipositor. It seems 

 impossible that its length, at least in the incipient stage could be of 

 any selective value, since most Hymenoptera provided with length- 

 ened ovipositor have developed no structures or devices of any kind 

 to permit of extensive retraction of this organ. iVfter what has been 

 said of the conditions prevailing in Dolichotrypes which have been 

 considered at some length, it is evident that a more extensive knowl- 

 edge of these minute Hymenoptera may lead to interesting conclusions 

 concerning the relation between the morphology of the body and the 

 function of oviposition. 



At the same time, it must be borne in mind that the horn of Ino- 

 stemma does not vary to any excessive degree and that its form and 

 size are at present as definite and clearly fixed in each species as are 

 the other parts of the body, and that they are not variable like the 

 abdominal segments of Dolichotrypes which have not yet attained 

 fixed dimensions. 



